Apparatus for controlling temperature

ABSTRACT

Apparatus for controlling temperature within a housing (200) comprises a thermal storage device (102) for maintaining a controlled temperature within the housing, and a thermal transfer arrangement (104) for selectively transferring heat between the thermal storage device and the external environment so as to effect thermal storage in the storage device, the thermal storage device comprising a thermal storage medium which is in direct contact with the thermal transfer arrangement. A further aspect of the invention is disclosed, in which a plurality of thermal storage devices are provided, each one being separate from the other such devices.

This invention relates to apparatus for controlling temperature within ahousing, and particularly to apparatus for the passive cooling ofequipment accommodated in such a housing. The invention also relates toa housing incorporating the apparatus.

In many technical areas such as telecommunications, fibre optic systems,meteorology, transmission and-data control, it is necessary to keepelectric or electronic equipment at remote locations. A desertenvironment is one typical location. The equipment is typically kept ina purpose-built, insulated, closed ambient housing (or shelter), oftenin adverse weather conditions. In order to ensure a high Mean TimeBetween Failure for such equipment, it is necessary to maintain theequipment at a near-constant temperature, and often between certaincritical temperature limits. At these remote locations, an externalpower supply is usually not available, and the equipment mayconsequently be solar-powered via photovoltaic cells. However, the powerfrom these cells is normally insufficient to power active coolingapparatus, such as an air conditioning system. Hence passive coolingapparatus is required in order to control the temperature of theenvironment in the housing.

Passive cooling apparatus is already known. It comprises essentiallythree main components, an insulated container (housing) to resist heattransfer from the external ambient, a thermal storage device formaintaining a controlled temperature within the housing and a thermaltransfer arrangement for selectively transferring heat between thethermal storage device and the external environment so as to effectthermal storage in the storage device.

In the known apparatus the thermal storage (accumulating) deviceincludes a thermal storage (accumulating) medium in the form of asubstance which changes its phase between solid and liquid at or nearthe desired temperature for the environment inside the housing.

The thermal storage medium inside the thermal storage device absorbs andaccumulates the heat given off from the electric/electronic equipmenthoused inside the container and the heat flowing through the wallsduring the hotter part of the day.

The thermal transfer arrangement comprises a conduit arranged in aclosed circuit and containing a thermal transfer fluid. The conduit isarranged such that inside the housing the fluid exchanges heat with thethermal storage device; it also passes out of the housing, upwardly andover the housing, where it is arranged such that the fluid alsoexchanges heat with the external environment.

During the part of the day when the external environment is hotter thanthe internal environment, no heat transfer takes place because thewarmer thermal transfer fluid outside is trapped in the portion of theconduit outside the housing. However, at night time or at other timeswhen the external environment is cooler than the internal environment,the colder fluid outside falls under gravity into the portion of theconduit inside, and cools down and regenerates (liquid to solid) thethermal storage medium inside the thermal storage device. Hence, thethermal storage medium inside the thermal storage device is regenerated(liquid to solid) by selective heat transfer between the storage deviceand the external environment, the selectivity of the apparatus beingreliant on the buoyancy force of natural convention of the thermaltransfer fluid.

In the known apparatus, a number of thermal transfer arrangements areprovided, each comprising a conduit in the form of a closed circuit inthis known apparatus, a large number of individual thermal storagedevices are provided. Each one comprises bonded sheets of metal in whichare formed individual pockets containing thermal storage medium. Thesame number of pockets is provided as thermal transfer arrangements. Thesheets of metal are sealed together around the pockets by a roll-bondingtechnique, in order to retain the medium. A hole is also formed throughthe centre of each pocket, the sheets of metal also being sealedtogether around the periphery of each hole. Each hole receives theconduit of its respective transfer arrangement. Heat transfer betweenthe conduit and the individual thermal storage device is effected byensuring a tight, friction fit between the conduit and the metal sheetsof the storage device.

As mentioned earlier, a large number of individual thermal storagedevices are provided. The devices are in fact mounted in parallel arrayalong the portions of the conduits inside the housing.

The known device suffers from two main drawbacks. Firstly, heat transferbetween the individual thermal storage devices and the conduits is notparticularly good, and hence the efficiency of the apparatus issignificantly lower than its theoretical maximum. Secondly, theapparatus lacks versatility, in that, once constructed, the number ofcircuits cannot easily be added to, the number being fixed by the numberof holes in the individual storage devices. The number of circuits mightneed to be increased if, for example, the housed electrical orelectronic equipment were to be upgraded, since upgrading might meanhigher heat dissipation from the equipment.

The present invention seeks to solve these or other problems. Accordingto a first aspect of the present invention, there is provided apparatusfor controlling temperature within a housing, comprising a thermalstorage device for maintaining a controlled temperature within thehousing, and a thermal transfer arrangement for selectively transferringheat between the thermal storage device and the external environment soas to effect thermal storage in the storage device, the thermal storagedevice comprising a thermal storage medium which is in direct contactwith the thermal transfer arrangement.

Since the thermal storage medium (thermal accumulator) is in directcontact with the thermal transfer arrangement, it has been found thatsignificantly improved thermal transfer can be achieved than waspossible with the known apparatus. In the known apparatus, thermaltransfer between the thermal storage medium and the conduit of thethermal transfer arrangement occurs via the metal sheets containing themedium, by means of a frictional fit between these sheets and theconduit. It has now been found that this frictional fit may in manycircumstances prevent satisfactory heat transfer between the twocomponents.

With the present invention, the ability to achieve better thermaltransfer between the thermal storage device and the thermal transferarrangement has the further advantage that the size of the thermalstorage device can be reduced due to the higher thermal efficiency ofthe apparatus.

Suitably, the thermal transfer arrangement includes a conduit fortransporting thermal transfer fluid, the thermal storage medium being indirect contact with the conduit. If so, preferably the thermal storagemedium completely surrounds the conduit, so that thermal transferbetween the two can be optimized. More preferably, the thermal transfermedium is contained within a sleeve which encloses a portion of theconduit. This has been found to be an effective way of putting theinvention into practice.

Preferably, the apparatus further includes at least one fin extendingthrough the thermal storage medium towards the thermal transferarrangement. This can ensure a good thermal transfer with the thermaltransfer arrangement. It can also assist in providing a uniformtemperature distribution within the thermal storage medium

For the same reasons, preferably the apparatus includes at least one finextending between the sleeve and the conduit through the medium.

The thermal storage device may have at least one outwardly projectingfin for transferring heat with the interior of the housing. This featurecan enhance the thermal transfer between the thermal storage device andthe interior environment.

According to a second aspect of the present invention, there is providedapparatus for controlling temperature within a housing, comprising aplurality of thermal storage devices for maintaining a controlledtemperature within the housing, and a respective thermal transferarrangement for each such thermal storage device, for selectivelytransferring heat between the thermal storage device and the externalenvironment so as to effect thermal storage in the storage device, eachsuch thermal storage device being separate from the other such devices.

By arranging for each such thermal storage device to be separate fromthe other such devices, effectively a plurality of distinct individualapparatuses for controlling the temperature inside the housing can beprovided. This has the advantage of greater versatility, since anindividual such apparatus can be added to or subtracted from the overalltemperature control apparatus relatively easily, in situ, in order toupgrade or downgrade the apparatus. Also, an individual such apparatuscan be replaced relatively easily if it becomes defective, withoutdisturbing the other such apparatuses and without involving stoppage ofthe remainder of the apparatus. This factor is extremely important, asit can avoid high temperatures damaging the sensitive and strategicelectric or electronic equipment housed inside the shelter. Malfunctionmay occur, for example, due to poor transportation of the apparatus,incorrect installation or acts of-vandalism or terrorism.

Thus the apparatus can be flexible and modular, and be easily designedaccording to the requirements of a specific location. It can besufficiently flexible to equip existing housings.

For ease of maintenance, preferably each thermal storage device consistsof a single container containing thermal storage medium. In thepreferred embodiment, each thermal storage device comprises a respectivesleeve containing thermal storage medium and enclosing a portion of thethermal transfer arrangement.

Again, for ease of maintenance, each thermal transfer arrangement isseparate from, or releasably connected to, the other such arrangements.Hence the entire individual temperature control apparatus is easilyseparable from the other such apparatuses.

Again for ease of maintenance, preferably the thermal transferarrangement includes at least one portion which is releasablyconnectable with the remainder of the arrangement. For instance, one ormore portions of the conduit external to the housing may be releasablyconnectable, to enable easy maintenance or replacement of theseportions. In particular, the external heat exchanger portion may be soconnectable.

The invention extends to a housing incorporating apparatus as aforesaid.

Preferred features of the invention are now described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of apparatus according to thepresent invention for controlling temperature within a housing;

FIG. 2 is a side elevational view of the apparatus shown incorporatedinto a housing, the housing being shown in section;

FIG. 3 is a side elevational view of the apparatus shown at a somewhatenlarged scale;

FIG. 4 is a cross-sectional view of the apparatus incorporated into thehousing, the cross-section being taken along the line XX' shown in FIG.2, only part of the housing being shown;

FIG. 5 shows to an enlarged scale a cross-section through an externalportion of the apparatus shown in FIG. 4; and

FIG. 6 shows to an enlarged scale a cross-section through an internalportion of the apparatus shown in FIG. 4.

Referring first to FIGS. 1 and 2, apparatus for controlling temperaturewithin a housing comprises generally four individual such apparatuses,each designated as 100. It will be understood that the number ofindividual apparatuses provided is not critical, and is dependent mainlyon the thermal performance necessary for thermal temperature control ofthe housing and also on the housing location itself. Each individualsuch apparatus includes a thermal storage device 102 and a thermaltransfer arrangement 104 which carries thermal transfer fluid (notshown). In this embodiment, the thermal transfer fluid is an aqueoussolution of 1,2-diols (dihydroxyl alcohols). An expansion tank 106, inthis embodiment of circular cross-section, and formed by extrusion isfixed onto the shelter by bracket 108. Pipes 110 lead from eachindividual thermal transfer arrangement 104 to the tank 106 and arereleasably connected to it by means of clamps (not shown). The expansiontank compensates for the variation in volume of the thermal transferfluid. Apart from having a common expansion tank 106, the individualapparatuses 100 are entirely separate. In an alternative embodiment,each individual apparatus could have a separate expansion tank.

As can be seen from FIGS. 1 and 2, the control apparatus is incorporatedinto a closed, monolithic, box-shaped housing 200, a portion of theapparatus being inside the housing, and a portion being outside. Thehousing includes thermally insulated panels 202 which act as a shelterfor electrical equipment 204. The panels are of a sandwich construction,the outer layers of the sandwich being aluminium or steel sheets,between which are sandwiched high density hot injected polyurethanefoamed under pressure. They are held together by an aluminium or steelframe. The external part of the apparatus is retained on the housing by,amongst other means, brackets 206.

An individual control apparatus 100 is now described in more detail withreference to FIG. 3. The thermal transfer arrangement 104 includes aconduit 112 in the form of a closed circuit. An external portion of theconduit acts as an external heat exchange device 114 for exchanging heatwith the external environment, and an internal portion of the conduitacts as an internal heat exchange device 116 for exchanging heat withthe thermal storage device 102 and with the internal environment.

The external and internal heat exchange devices 114 and 116 areconnected together via two curved, sealed pipes 118 forming part of theconduit. The pipes are covered with insulating material 120, part ofthis material being shown cut away in FIG. 3. The pipes are releasablyconnected to the heat exchange devices 114 and 116 by releasablecouplings 122 made of reinforced rubber, each coupling being fastened toits respective pipe and heat exchange device by two or more clamps (notshown) which in the preferred embodiment are made of steel. Thecouplings 122 are again covered with insulating material 124, part ofthis material being shown cut away in FIG. 3.

The insulating material 124 is not of a particularly heavy grade, andhence is easily removable to expose the releasable couplings 122.

It will be apparent that the heat exchange devices 114 and 116 areeasily and repeatably removable from the remainder of the controlapparatus 100. This is achieved by loosening the various clamps andcouplings, and removing the pipes 118. The external heat exchange device114 can then be removed very easily. The internal heat exchange device116 is configured to be easily removable by being slid lengthways to itsfarthest extent. Its distal end is then released from its aperture inthe panel 202. The heat exchange device can then be removed by acombination of a pivotal and a sliding movement.

In the apparatus of the present invention, since the thermal transferfluid is essentially at atmospheric pressure, the couplings 122 do notreed to be able to withstand any substantial pressure. Nevertheless, toprevent any possible leakage of the thermal transfer fluid damaging theequipment 204 within the housing 200, any necessary releasable couplingis located outside the housing. There are no releasable couplings withinthe housing.

An inlet/outlet valve 126 is provided on the apparatus 100 for thefilling and emptying of the thermal transfer fluid in the circuit duringinstallation, repair or replacement of the apparatus.

With the heat exchange devices of the apparatus of the presentinvention, no evaporator or condenser units are required, and hence theapparatus operates in a relatively simple fashion. The thermal transferfluid does not change phase during normal operation of the apparatus,and is maintained substantially at ambient pressure by means of theexpansion tank 106, which is open to the atmosphere.

An important feature of the hydraulic circuit, constituted by theconduit 112, in which the thermal transfer fluid flows is that it is inthe form of a single, smooth, continuous, roughly oval-shaped loop. Asviewed from within the loop, all the components of the loop (the heatexchange devices 114 and 116 and the sealed pipes 118) are eitherstraight or concave; there is no reverse curvature anywhere on the loop.This can ensure a satisfactory flow of thermal transfer fluid in thehydraulic circuit. A further feature which can ensure satisfactory flowis that the conduit 112 is of relatively large internal diameter, tominimize hydraulic losses. In order to ensure the uni-directionallty ofthe flow, the heat exchange devices 114 and 116 are very slightlyinclined with respect to the horizonal. The expansion tank 106 issuitably located near the uppermost point of the hydraulic circuit.

The thermal storage device 102 is now described in more detail withreference in particular to FIGS. 3 to 6. The device comprises acontainer in the form of a circular cross-section sleeve 128 whichextends the length of the internal heat exchange device 116 so as toshroud it concentrically, and which is sealed thereto at each of itsends. The interior annular space in the sleeve is filled with thermalstorage medium (not shown), so that the medium is in direct contact withthe conduit. Hence thermal transfer can occur by conduction between thethermal transfer fluid and the medium.

The thermal storage medium is of a type which changes phase from solidto liquid at a selected temperature of interest. It thus acts as anefficient thermal "capacitor" of high enthalpy. For use in the desert,for example, the selected temperature might be in the range 35 to 50° C.The medium might typically be a stable, organic phase change compound.It would suitably be a compound derived from a lubricating oil fractionand containing large amounts of long-chain alkanes. Such a material hasan almost indefinite life and is non-corrosive.

The thermal storage device 102 for each individual control apparatus 100consists of a single container. This can afford a versatile arrangementin which the individual apparatus is easily removable or replaceable.Use of a single container also means that the thermal transfer fluid isnot required to traverse any tortuous route through the thermal storagemedium.

As shown in the various figures, a helicoidal fin 130 is provided on theexternal surface of the conduit 112 as part of the external heatexchange device 114, and extending along the length of this device 114.The fin assists heat transfer with the external environment. A similarhelicoidal fin 132 is provided on the external surface of the sleeve128, to assist heat transfer with the internal environment.

To assist heat exchange between the thermal storage device 102 and thethermal transfer arrangement 104, there is provided in the space betweenthe sleeve 128 and the conduit 112 a set of helicoidal fins 134 whichare in contact with the conduit 112 and extend out through the thermalstorage medium to the wall of the sleeve 128. The fins 134 are woundtightly onto the conduit 112 so as to be in close frictional contacttherewith; equally, the sleeve 128 is a tight fit over the fins. Usuallyjust a single strip of metal is employed to make up the set of fins 134,but more than one strip may alternatively be employed.

It has been found pursuant to the present invention that the geometryand configuration of the fins 134 is important for the correctfunctioning of the apparatus of the present invention. In the firstinstance, it Is important that the fins are in contact both with theconduit 112 and the sleeve 128. This can achieve optimum, homogeneousheat transfer, and can also ensure that the thermal transfer fluid canexchange heat via a relatively direct route with the atmosphere insidethe housing 200 as well as with the thermal storage medium.

Preferably the fin or fins are aligned neither with the longitudinalaxis of the conduit 112 nor with its transverse axis, so that heat canbe transferred both circumferentially around the thermal storage mediumand also along it.

The total number of turns of the helicoidal fins, for all the finscombined, is preferably not more than 10%, but greater than 3 or 5%, ofthe length of the thermal storage device 102 in millimetres. The pitchbetween adjacent turns is preferably between 2 and 20%, more preferablybetween 4 and 15% of the diameter of the conduit 112. For a standardsize of apparatus, with the diameter of the conduit 112 being between 8and 20 cm, preferably between 10 and 15 cm, the pitch would suitably bein the region of 5 to 20 mm. Amongst other factors, the characteristicsof the phase change material have been found to influence the optimumpitch. Again, the thickness of the individual fins is preferably greaterthan 0.25%, but less than 0.5%, of the diameter of the sleeve 128. For astandard size of apparatus, the fins might suitably have a thickness ofabout 1 mm. The above dimensional ranges have been found to afford theoptimum thermal characteristics for the apparatus.

Further fins 136 and 138, which are star-shaped in cross-section,respectively extend lengthwise the length of the external and internalheat exchange devices 114 and 116 and are mounted in the interior of theconduit 112 in these regions. The conduit is circular in cross-sectionand of uniform diameter in these regions. These features can assure themaximum hydraulic and mechanical continuity between the external andinternal parts of the thermal transfer arrangement 104.

The overall principles governing the operation of passive coolingapparatus have been described in relation to the known passive coolingapparatus. These principles also apply to the present invention.

The temperature control apparatus as described above possesses manybeneficial characteristics, such as operation without primary powersources, an absence of moving mechanical or electrical parts, the factthat no part of the apparatus is under a pressure higher than that ofatmospheric or of the column of static thermal transfer fluid, and thefact that the thermal transfer arrangement is in direct contact with thethermal storage medium and therefore the heat exchange is made byconduction and not convection or irradiation, hence leading to animproved thermal exchange efficiency. Also, the organic substance usedas the thermal storage medium is stable and has an unlimited life; it ischosen and blended so as to help prevent an increase above the criticalmaximum internal temperature limits allowed inside the housing when thethermal transfer with the external environment is not activated due tothe external ambient conditions. This thermal storage mediumsubstantially reduces the difference between the internal maximumtemperature during the day and the minimum at night, thereby increasingthe Mean Time Between Failure factor and avoiding thermal andconsequential mechanical stress that would result in a shorter life ofthe equipment inside the housing.

It will be understood that the present invention has been describedabove purely by way of example, and modifications of detail can be madewithin the scope of the invention. For example, the housing 200 could beprovided with, say, three instead of four individual controlapparatuses, but with room being left for a fourth such apparatus to befitted at a later time if required It will also be understood that thenumber of individual control apparatuses depends mainly on the thermalperformance necessary for internal temperature control of the housingand also on the housing location itself. Any number up to, say, six (oreven higher) might be appropriate according to the thermal design.

Each feature disclosed in the description, and (where appropriate) theclaims and drawings may be provided independently or in any appropriatecombination.

What is claimed is:
 1. A housing having a base, side walls and a roofand incorporating one or more apparatus for controlling temperaturewithin the housing, each said one or more apparatus comprising:a thermalstorage device for maintaining a controlled temperature within saidhousing, and a thermal transfer arrangement for selectively transferringheat between the thermal storage device and the external environment,according to the relative temperatures of the thermal storage device andthe external environment, so as to effect thermal storage in the thermalstorage device, said thermal transfer arrangement comprising:a firstheat exchange device within said housing for exchanging heat with saidthermal storage device, a second heat exchange device, external to thehousing, for exchanging heat with the external environment, and aconduit, in the form of a continuous closed loop, for transporting athermal transfer fluid between said first and second heat exchangedevices; a support assembly disposed on the roof of said housing forsupporting said conduit and said second heat exchange device, wherein:aremovable part of the conduit, which forms the first heat exchangedevice, extends through apertures passing through side walls of thehousing and also has distal portions extending outside the housing sothat any leakage of the thermal transfer fluid occurs outside thehousing; the distal portions extend beyond the side walls by an extentselected such that the first heat exchange device is supported by theside walls but can also be removed by sliding it lengthways to releaseone of said distal ends, inside the housing, from its side wallaperture, and releasable couplings are provided for the distal portionsof the conduit both so as to facilitate (a) removal of said first heatexchange device, and (b) connection to the second heat exchange device,which is formed by another part of the conduit external of the housing.2. The housing according to claim 1, further comprising one of anexpansion tank connected to said at least one apparatus, and a thermalfluid expansion tank connected to each said at least one apparatus. 3.The housing according to claim 1, wherein the thermal transferarrangement includes only one heat exchange device external to thehousing.
 4. The housing according to claim 1, further comprising aninlet/outlet valve provided on the thermal transfer arrangement, saidvalve being external to the housing.
 5. The housing according to claim1, wherein the thermal transfer arrangement is adapted to cool down thethermal storage device.
 6. The housing according to claim 1 wherein saidthermal transfer fluid does not change phase during normal operation ofsaid one or more apparatus.
 7. The housing according to claim 1, whereinthe releasable couplings are made of a resilient material.
 8. Thehousing according to claim 7, wherein the releasable couplings arejoined to U-shaped parts of the conduit which communicate between thefirst and second heat exchange devices.
 9. The housing according toclaim 8, wherein the part of the conduit which forms the second heatexchange device is supported by brackets on the housing, and the firstand second heat exchange devices are self-supported respectively by saidhousing side walls and said brackets when the releasable couplings areremoved.
 10. The housing according to claim 1, wherein the thermalstorage device comprises a sleeve enclosing a portion of the conduit andcontaining a thermal storage medium, and at least one fin extendsbetween the sleeve and the conduit through the medium, and wherein eachsaid at least one fin is aligned neither with the longitudinal nor withthe transverse axis of the portion of the conduit.
 11. The housingaccording to claim 10, wherein the sleeve includes at least oneoutwardly projecting fin for exchanging heat with the interior of thehousing.
 12. The housing according to claim 1 wherein the conduitcontains at least one fin.
 13. The housing according to claim 1, furthercomprising a plurality of first heat exchange devices and respectivethermal storage devices, and wherein said plurality of first heatexchange devices are releasably connected to respective second heatexchange devices which are external to the housing.